Methods for decorating plastic and rubber surfaces with printed films are matters of common knowledge and experience.
For example, transfer printing papers for plastics are commercially available, and they are useful for the fast, efficient and inexpensive decoration of poly(vinyl chloride) and polyurethane materials, by way of illustrative examples. With such films, rigid plastics can be printed with perfect register and without distortion. On the other hand, with rubbery substrates, and especially with heat-cured rubbery polymers, such films may not be used because the extensiblilty of the rubber and the heat used in molding leads to serious problems with distortion and adhesion.
Representative of the current state of the art of in-mold decoration of vulcanizable rubbery substrates are Komatsuzaki, EPO Published Patent No. 0,346,474, Dec. 20, 1989, and Hinishi, Japanese Patent Publication No. SH056-146,717, Nov. 14, 1981.
In the EPO application, a heat resistant flexible plastic film is used as a transfer plate for in-mold printing, simultaneous with shaping of a contact rubber body. A complex three-part mold is used, one part of which is used to keep the transfer film out of contact with the curable rubber, and this assists in keeping the print from smearing. It is, however, difficult in practice to keep the print from flaking off of the rubber because the heat used during molding and vulcanization interferes with adhesion.
The in-mold decorating of synthetic resins and rubbers with less complex molds and dry transfer films is also described in the above-mentioned Japanese Patent Publication in which there is used a transfer film (1) having at least a release coating layer (3), printing ink layer (4), and adhesive coating layer (5) on a substrate film (2). The transfer film is cut to suit the outside size of a molding to be formed, and is fitted into a mold (6). A resin molding is then formed, and the adhesive layer (5), printing ink layer (4) and release layer (3) are transferred onto the surfaces of the molding. After forming, the substrate film (2) only is removed, thereby forming continuous decoration, e.g., in the bottom and sides of the molding. Because, however, the release layer stays on the outside of the molded article there is a serious drawback, and that is the tendency of water to bead on the decorated surface, causing safety problems and slippery conditions when, for example, in-mold decorated bath mats, and the like are made with such transfer films. Moreover, the decoration is affixed to the article by means of an adhesive which necessarily must develop enough bond between the substrate and the print layer to assure permanency. This is difficult to accomplish during molding because the plastic must flow to fill the mold and the lateral shearing stresses developed between the adhesive coating layer (5) and the printing ink layer(4) have been found in practice to exhibit a strong tendency to distort the image.
It has now been found that if the procedures of the prior art are modified to eliminate all use of an adhesive layer, and if the thin resin film is replaced by a thin discontinuous pattern printed with an ink comprising a pigment and/or dye and a polymeric vehicle, and if the substrate paper or film is provided with a printable controlled release surface of a judiciously selected type, then, in contrast to the Japanese Patent Publication disclosure, the substrate film and the controlled release surface both are removed, leaving a non-slippery decorated article. Furthermore, if the polymeric vehicle for the ink is judiciously selected, the decoration will adhere semi-permanently to the controlled release surface during molding, thereby permitting the ink to transfer and embed itself into the molded article without distortion due to shearing in the mold and without the need later to rely on any adhesive for permanently bonding the decoration to the article. Semi-permanent adherence is easily determined, for example, by lifting with pressure sensitive tape in accordance with well-established procedures in this art.